CHICAGO - With early voting starting Monday, the four Republican candidates for Illinois governor were campaigning throughout the state Saturday, encouraging their supporters to cast a ballot before the March 18 primary.

Businessman Bruce Rauner, Treasurer Dan Rutherford, and Sens. Kirk Dillard and Bill Brady hope that locking in votes early in what's usually a low-turnout election will boost their chances of winning their party's nomination to take on Democratic incumbent Pat Quinn. However, getting Republican voters to cast ballots ahead of the traditional Election Day has proved difficult.

Brady said his campaign is trying to motivate early voting through social media, particularly Facebook and Twitter.

"The message we are sending is that we are the only reliable Republican in this race," said Brady, who won the GOP nomination in 2010 and was campaigning in central Illinois.

Rauner was on his campaign bus and planned to make stops in central and southern Illinois. Campaign aide Mike Schrimpf said Republicans haven't been good at turning out early voters because the party hasn't been organized at the grass-roots level.

Rauner has made it a priority to not just run television ads, but to run a comprehensive campaign, Schrimpf said. Since the campaign began, volunteers have made 120,000 telephone calls.

"Not all just about early voting, but clearly an indication of a strong grass-roots operation," he said.

"We are trying to run a great campaign," Rauner said, noting that turnout is generally low in the GOP primary. "Getting out the vote is critically important. This is a critical election. We have to get Pat Quinn out of office."

Rutherford's campaign planned to remind supporters of the start of early voting with telephone calls and emails over the weekend, spokesman Brian Sterling said.

Rutherford declined to be interviewed on the effort. He's skipped reporters' questions after candidate debates - most recently Thursday evening in Chicago - as he's faced allegations of misconduct and had to defend himself on the campaign trail. A former employee filed a federal lawsuit accusing Rutherford of sexual harassment and being forced to do campaign work on state time. Rutherford has dismissed the allegations as false.

Dillard campaign manager Glenn Hodas said the campaign is emailing supporters, asking them to vote early and pointing out locations where they can do so. The last GOP gubernatorial primary was decided by fewer than 200 votes, so getting people to the polls could be a deciding factor.

"We are expecting the race to become significantly closer," he said.

Quinn, a Chicago Democrat, is seeking re-election. He has one lesser-known challenger, anti-violence activist Tio Hardiman of suburban Chicago.

Politicians aren't the only ones pressing voters to cast early ballots. The Illinois Coalition of Immigrant and Refugee Rights is canvassing the immigrant community to encourage early voting.

"It's important that lawmakers hear from us," CEO Lawrence Benito said. "The earlier they get out and vote, the easier it is for us to focus on getting more people to the polls."

Because of the organization's reputation for taking on tough fights, including advocating immigration reform on the federal level and pushing for driver's licenses for those who entered the country without legal permission, he said it has the credibility to sell early voting to those who usually wait until Election Day.

In addition to early voting in person, registered voters can cast absentee ballots or vote by mail. Eligible voters also can register or change their address through March 15. Participants in the grace-period registration must cast their ballots at the election board office and are ineligible to vote early or cast a ballot at a polling place.